Many industrially important processes result in the production of streams of carboxylic acids in dilute concentrations. Economic considerations and environmental concerns lead to the desirability of recovering carboxylic acids from such streams for reuse, for sale, or for disposal in the most economic manner.
Experience has shown that carboxylic acids in dilute concentrations, i.e. below about fifteen percent (15%) by weight, in aqueous streams, are most economically removed and recovered through the use of a liquid-liquid extraction process employing a high-boiling solvent. When the carboxylic acids make up less than about three percent (3%) by weight of the stream to be treated, it becomes difficult to recover the acids economically by such a liquid-liquid extraction process, although environmental considerations often make it necessary to treat such streams nonetheless. In accordance with the present invention, methods and apparatus are provided for pre-concentrating dilute carboxylic acid streams having a low concentration of acids, following which the relatively more concentrated streams so produced are further treated, as by liquid-liquid extraction to recover the carboxylic acids they contain with better economic performance.